<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>太极</title>
    <style>
      .taiji {
        margin: 0 auto;
        margin-top: 100px;
        width: 400px;
        height: 400px;
        box-sizing: border-box;
        border-width: 1px 1px 200px 1px;
        border-color: black;
        border-style: solid;
        border-radius: 50%;
        position: relative;
      }
      .taiji::before {
        position: absolute;
        content: '';
        width: 50%;
        height: 100%;
        background-color: #fff;
        left: 0;
        top: 50%;
        border-radius: 50%;
        box-sizing: border-box;
        border: 50px solid #000;
      }
      .taiji::after {
        position: absolute;
        content: '';
        width: 50%;
        height: 100%;
        background-color: #000;
        right: 0;
        top: 50%;
        border-radius: 50%;
        box-sizing: border-box;
        border: 50px solid #fff;
      }
    </style>
  </head>
  <body>
    <div class="taiji"></div>
  </body>
</html>
